Almost nothing happens in this small poem, and that is part of its charm. A wren lands on a verandah, finds half a walnut shell lying upside down, and inspects it carefully, hopping around it and poking into each of its two openings. The speaker simply watches, noticing the bird's "big clown feet" and the way it leaves "nothing to chance."
The tone is gentle and quietly humorous. The shell becomes a "round kayak," a playful comparison that turns a bit of leftover food into a tiny boat. The ending is where the mood deepens. Tea time arrives, but "nobody came," which suggests an absence, perhaps a lonely or still house. After the wren leaves, the shell rocks and settles, "riding high / without ballast." The image feels peaceful, but also a little empty, like the afternoon itself. The speaker seems content to notice small things, though a faint stillness lingers underneath.